- Justin Schaub
BUSHINGS EXPLAINED: POLYURETHANE vs UHMW
Updated: Dec 10, 2022
There is no doubt that the older BMWs we have come to love, are some of the best examples of automotive engineering of their time. As time passed, we got to enjoy the fruits of depreciation and are able to buy what was a $60,000 M3, for less than $10,000. With all of this great pricing, comes also another price…maintenance.
We could go on and on about all the different components of the car that should be looked at, but in this blog we are focusing on bushings. The various bushings in the car are wear components, they aren’t meant to last forever. Bushings are there to absorb shock, or act as a mediator component between two moving surfaces (IE control arm). The stock bushings from BMW usually consist of a hard rubber, and over time can compress, crack, and simply wear out causing clunking, steering components from being out of alignment, and frankly less than desirable driving experiences.
If you are restoring a car, I would 100% replace these components back with brand new factory bushings and mounts, but thanks to companies like Revshift, we have other options on the market. Revshift offers premium polyurethane upgrades in various hardnesses that will not only make your bushings last longer, but stiffen up your suspension if you desire for activities like track use. With all of this, comes confusion. There are so many different options, so we decided to break these down for you, so you can make the best decision for your car.
80A black polyurethane suspension bushings are slightly stiffer and stronger than the OEM rubber but will not cause additional noise or vibration. They are a great choice as an upgraded stock replacement which is why we refer to them as having an OEM+ feel. 95A green polyurethane bushings are significantly stiffer and stronger than the OEM rubber and may transmit some minor noise and vibration. They are an excellent choice for enthusiastically driven street cars and track cars. 70D white polyurethane bushings are solid but still absorb some noise and vibration. The hardness is comparable to delrin or UMHW. They are most commonly used on dedicated track cars.
Motor and transmission mounts differ from suspension bushings when it comes to choosing hardness because the engine is the main source of vibration. Harder motor and trans mounts will transmit more vibration at idle into the vehicle's cabin. The harder the mounts, the more vibration at idle you will feel. If increased vibration is a concern then we recommend our 80A black polyurethane mounts. They are slightly stiffer than OEM rubber mounts so a small increase in vibration at idle may be noticeable at first but it typically becomes less apparent over a short amount of time driving.
Important: Revshift recommends either matching the hardness of your motor and trans mounts or choosing harder motor mounts with softer trans mounts. Installing harder trans mounts with softer motor mounts will result in more vibration being transferred through the trans mounts. It also puts a lot of extra load on the trans mounts and the transmission mounting points because the weight of the engine moving around on the softer motor mounts is being directed to the harder trans mounts.
NVH FROM MOTOR / TRANS MOUNTS VS SUSPENSION BUSHINGS
The goal of stiffening up the motor and transmission mounts is to reduce the movement of the drivetrain. This results in better handling and more power being directed toward the wheels. Motor and trans mounts are the most responsible parts for transmitting NVH (noise, vibration, harmonics) into the vehicle’s cabin. In other words, the harder you make the motor and trans mounts, the more vibration you will feel.
Suspension bushings are much more forgiving in regard to NVH. Most of the road noise and bumps are dealt with by your springs and shocks. Stationary mounting bushings such as subframe and differential bushings can be very stiff without noticing much of a difference in ride harshness. Rotational bushings such as control arm and trailing arm bushings are a little more noticeable the stiffer you go but still do not significantly impact ride comfort for the performance-minded driver.
For a high-performance street car, Revshift generally recommends their 80A motor and trans mounts and our 95A suspension bushings. This combination will minimize NVH and reduce drivetrain movement as well as significantly improve the vehicle’s handling by stiffening up the suspension bushings.
Pro tip: In general, if you want to reduce vibration being transferred through the motor mounts at idle, raise your vehicle's idle RPM to 800-900 RPM. This speeds up the frequency of the vibrations and smooths things out a bit.
WHAT IS REVSHIFT POLYURETHANE?
Revshift bushings are made from extremely high grade polyurethane. The high quality, proprietary polyurethane compounds that we use are among the best for automotive use and exceed the material quality of possibly all other automotive polyurethane manufacturers.
There are hundreds of different formulations of polyurethane for various uses. They work with a top American chemical company to formulate a specific type of polyurethane that is best for their use in high performance automotive suspension. We process the raw materials in our own facility and cast the parts in special molds that we design and produce ourselves.
Polyurethanes are a group of organic polymers that are normally grouped with rubber. They are elastomers which are stretchy materials. Our unique manufacturing process has proven itself to be a superior method of producing high end customized elastomers with adjustable properties.
Revshift polyurethane can be tuned to produce polymers of different hardness and physical properties to suit the specific application.
Revshift polyurethane is elastic and can absorb an enormous amount of trauma without permanently deforming (unlike UHMW and Delrin).
Revshift polyurethane is resistant to water, oil, gasoline, salt, antifreeze, and most solvents (unlike rubber).
Revshift polyurethane is half the weight of aluminum and about 20% lighter than rubber.
POLYURETHANE VS UHMW / DELRIN
We are often asked: “What is the difference between Revshift polyurethane bushings and the white uhmw (ultra high molecular weight polyethylene) bushings being sold on the internet?”. Uhmw is a cheap type of prototyping plastic. Uhmw material is not appropriate for automotive use because it does not return to its original shape when it is deformed.
That means, over time, uhmw bushings get compressed and loose on the vehicle. This results in clunking, incorrect suspension geometry, and a harsh ride. Uhmw is only available in one hardness / grade and that’s it. Other brands choose this material simply because the material is cheap to purchase, and the manufacturing is extremely easy to perform.
Revshift’s polyurethane is an elastomer so when it deforms it does return to its original shape. That means when your suspension squishes the bushings bounce right back to where they are supposed to be. That is proper suspension dampening and the goal of using bushings in the first place. We offer three hardness options to accommodate your needs. The hardest (70D white) is comparable to the uhmw hardness but our polyurethane is far beyond stronger and more resilient than uhmw.
If you know the facts about the two different materials then it’s a no brainer. Revshift’s bushings are higher quality, stronger, more reliable, and a better fit. Now you know.
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